In the oil industry there is in various situations a need to measure the composition and individual flow rates of a mixture of gaseous hydrocarbons, liquid hydrocarbons (oil or condensate) and water, flowing in a pipe. The conventional technique is to separate the fluid in a separator and to measure the flow of each of the components separately. During the last years also so-called multiphase meters have become available, which measure the composition and the flow rates without prior separation [1]. A special case of a multiphase flow is the so-called wet gas flow, which means that the fluid mixture is dominated by the gas phase containing small amounts of liquids. The liquid phase consists of water and of light liquid hydrocarbons (so-called condensate). Usually in a wet gas, the GVF (Gas Volume Fraction) is higher than about 95% vol. When measuring in a wet gas flow application using a multiphase meter, the relative uncertainty achievable for the liquid component flow rates is too high.
This applicant has recently developed a wet gas meter that is capable of measuring the water content of a wet gas stream using microwave technology and the wet gas flow rate based on a differential pressure device [2,3]. The amount of liquid hydrocarbons (condensate) has in this first generation wet gas meter been calculated rather than measured. The calculation is based on a priori knowledge about the molecular composition of the hydrocarbon mixture (gas and condensate), using a PVT software package (computer software tool used to calculate thermodynamic properties like densities and gas/liquid ratios of fluids at given temperatures and pressures).